In a general wireless communication system, only one carrier is mainly considered even though uplink and downlink bandwidths are differently configured. For example, a wireless communication system in which the number of carriers constituting each of uplink and downlink is one and an uplink bandwidth and a downlink bandwidth are generally symmetrical may be provided based on a single carrier. However, frequency allocation of a wide bandwidth is not easy except in some areas of the world. Accordingly, as a technique for efficiently using a fragmented narrowband, a carrier aggregation (also called bandwidth aggregation or spectrum aggregation) technique producing an effect as if a broadband is logically used by physically aggregating a plurality of bands in a frequency domain has been developed.
Carrier aggregation has been introduced to support increased throughput, prevent cost increase caused by introduction of a broadband RF element, and ensure compatibility with a conventional system. Carrier aggregation may include a technique supporting a system bandwidth of up to 100 MHz using multiple carriers even if one carrier supports, for example, a bandwidth of 5 MHz, 10 MHz, or 20 MHz. In addition, in a carrier aggregation technique, asymmetrical bandwidths may be allocated to uplink and downlink.
In a multi-carrier support system, a Mobile Station (MS) supporting multiple carriers may transmit and receive data through one or more carriers. The maximum number of carriers that can be used by the MS may differ according to the performance or capacity of the MS. Alternatively, the maximum number of carriers provided to the MS may be determined according to a Base Station (BS) policy. The MS needs to efficiently manage multiple carriers that can be used thereby.